Severe Storms for Denver Today with Large Hail and Possibly a Weak Tornado or Two

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UPDATE — THE NATIONAL WEATHER SERVICE HAS ISSUED A TORNADO WATCH FOR THE DENVER METRO AREA AND MOST OF THE EASTERN PLAINS UNTIL 9PM. THIS MEANS THAT CONDITIONS ARE RIGHT FOR TORNADOES TO FORM. tornadowatch
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We’re in the heart of Colorado severe weather season and leading up to this point, we’ve been relatively quiet. The occasional severe storm with hail or strong wind has swiped across the metro area before heading out east, but our severe weather seems to be a lot quieter than at this same time last year. Today, however, that looks to change. Denver and the surrounding areas have an Enhanced risk of thunderstorms today as put out by the Storm Prediction Center. This is something that generally only happens once or twice per year in Denver and is generally a good indication that we are in for some intense weather.

Enhanced

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Timing and Risks

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A line of storms has already developed to the south and west of Denver along the foothills and looks to be growing to the north. We’re going to start seeing storms develop around Denver and they’ll really pick up in intensity around noon.

Currently, it’s looking like the most significant storms will come through the area around noon and will be followed by a secondary push around 4pm after which storms will continue through tonight. The area at highest risk for damage from the storms is southeastern of Denver in areas like Highlands Ranch, Parker, Centennial, and extreme southeastern Aurora.

The atmosphere has plenty of moisture at the mid to upper levels which means that our most significant threat will be large hail. The latest models show that we lack a lot of the lower level shear (rotation from wind) to support intense tornadoes, however, we will have a southeasterly component to our wind which means that the Denver Convergence Vorticity Zone (DCVZ), which is an area where winds of opposing directions create rotation, will exist to the east of Denver. This area that extends northward along the I-25 corridor from Castle Rock to Denver and eastward from Denver to Limon is notorious for spawning weak landspout tornadoes and should be watched closely this afternoon. With that said, hail will be the primary threat followed by possibly strong and damaging winds. The NWS has not issued a tornado watch at this time. Tornadoes should be limited and, based off of current models, will be weak if they develop at all.

Chance of Thunderstorms, then Heat!

Thunderstorms are expected to develop in the evening hours on Monday, with a better chance of rain on the South and West sides of town. There is also a chance of storms in the afternoons on Tuesday and Wednesday. Some storms could be strong with high winds and decent sized hail on Tuesday if they are able to get going. Temperatures should be in the low to mid 80’s for highs each day. The weather will turn hot with temperatures around 90 from Thursday through the weekend. An approaching system may cool us down a bit next Monday. There will be a small chance for storms each day, mainly in the mountains and on the Palmer Divide.

Enjoy the weather and don’t forget the sunscreen!

Denver’s June Weather

June is typically warm and pleasant in the Denver area, with average highs ranging from the upper 70’s at the start of the month to the mid 80’s at the end of the month. Rainfall usually comes in the form of thunderstorms, some of which can be severe as June is part of Denver’s severe weather season. Cold fronts coming from the north bring cooler temperatures, but can also enhance the severe weather threat a day or two later, as moisture sometimes is pushed into the area from easterly winds. June can also feature very hot temperatures, as was the case in 2012 when Denver tied its all-time record high of 105º F, two days in a row on the 25th and 26th in a 5 day heat wave featuring highs above 100 every day.

The intense El Nino event that occurred over the last year has weakened rapidly and will likely transition to a La Nina in the fall and winter. The ENSO cycle as it’s called, can lead to changes in the upper level weather patterns across the globe, including the US. Comparing four previous years with a transition from El Nino to La Nina conditions in the summer (1988, 1998, 2007, 2010). Warmer than normal temperatures occurred in the center of the country, with Denver averaging about 1.4º F warmer than average on those years (Figures 1 and 2). Rainfall was also less than normal during these transition years, averaging about 0.7 inches less (Figure 3). Denver’s average June rainfall is just under 2 inches, which translates to about a third less rainfall than normal during the transition years.

JuneSfcTempMean

Figure 1 Average Air Temperature for June in Celsius. (16C = 61F)

JuneSfcTempAnom

Figure 2 Difference from Average Temperature During Transition Years (Warm colors are hotter, cool colors are colder)

JunePrecipAnom

Figure 3 Difference from Average Rainfall During Transition Years (Warm colors show less rain, cool colors are more)

2016 Outlook

(A brief explanation of what upper level ridges and troughs mean: Ridges are usually associated with dry and warm weather, while troughs are associated with cooler and more unsettled weather.)

Looking ahead to this June, weather models show a ridge in the jetstream to the west and near our area for about the first 10 days, indicating generally dry and warm conditions (Figure 4). That could change around the 8th, when we could see a weather system bring us a few thunderstorms and cooler temperatures. A stronger system is predicted to move into our area around the 10th, bringing cooler temperatures and the chance for more precipitation. Beyond this, the GFS (a mid range weather model) has a general ridge centered over us or just to our west mid-month, while the CFS (a long range climate model) has a ridge centered to our east. Both models have warm temperatures either way.

RidgeTrough

Figure 4 Jetstream on June 5th

Looking farther out gets tricky, as models rarely make the correct forecast. However, the CFS does a pretty good job at predicting general trends, and it has been showing an upper level ridge centered to our east and a trough to our west for most of the remainder of June. If this verifies, we could see generally warmer conditions to finish the month. (Sounds a lot like the pattern in the previous transition years doesn’t it?)

The Climate Prediction Center is calling for a warmer first half of June, with about average precip. The rest of the month is shown to have equal chances of above or below temperatures and precipitation. Only time will tell!

 

Enjoy the weather! I will likely be posting monthly outlooks and other interesting events in the future.

Jon

 

For more info about these topics check out:

(El Nino Discussion) http://www.cpc.ncep.noaa.gov/products/analysis_monitoring/lanina/enso_evolution-status-fcsts-web.pdf

(Climate Re-analyzer) http://www.esrl.noaa.gov/psd/

(Forecasting) http://www.weather.cod.edu/forecast/

 

 

Severe Thunderstorms Today for Denver and Parts of Northeastern Colorado

 

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Tornado near Cheyenne Wells, Colorado May 9th, 2015

Well, we’ve arrived in severe weather season and, while it has been roaring in the central high plains for a while, it’s starting to pick up in Colorado now. We’ve already seen a few tornadoes in extreme eastern Colorado and now it looks like the hail, wind, and tornado threats are starting to move to the west and will be in the front range before too long. While June is typically the busiest month for severe thunderstorms and tornadoes in Colorado, May has its fair share of wild weather events and serves as an introduction for the season.

Today we’ll start our severe weather season for the Denver metro area with a small chance of some hail and high winds although any significant hail and any tornadoes should stay to the east of town along I-76. High moisture in the region will feed storms that currently look like they’ll start on the eastern side of the metro area. On days when we see southeasterly winds (from the southeast), a feature called the “Denver Cyclone” tends to develop which is a broad circulation of air caused by our unique terrain that spins counter-clockwise. The Denver Cyclone aids in the development of thunderstorms and can develop areas of colliding air that produces tornadoes around Aurora, Parker, and Elizabeth. Today, however, any tornado threat should be along I-76.

Understanding Thunderstorm Threats

Below is the Storm Prediction Center’s storm outlook for today. The different categorical outlooks are familiar for those that have lived in places like Texas, Oklahoma, and Kansas. However, those of us that have lived in Colorado or in other locations may not be as familiar with the classification system. The Denver area and the northeastern Colorado plains is under a slight risk area which means that there could be hail between 1-2″, damaging winds, and one to two tornadoes. The I-76 corridor is under an enhanced risk for severe storms which means that severe storms will be fairly widespread, damaging hail and wind reports will be common, and a few tornadoes are possible. A graphic describing severe thunderstorm threats has been added below. The threat category colors correspond to the colors on the map.

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SPC’s Severe Weather Outlook for May 24, 2016

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Forecast

Storms will develop to the east and north of the Denver area early this afternoon between 1-2 pm local time. These storms will intensify and will follow the I-76 corridor to the northeast and will eventually turn into a line of storms that exits the state into Nebraska and Kansas. A primary storm will have the possibility to produce large hail, strong damaging winds, and a few tornadoes. Towns in the immediate impact area include Akron, Brighton, Brush Lochbuie, Fort Morgan, Holyoke, Sterling, Wiggins, Wray, Yuma.

Updates will be made during the day as storms occur. Ask any questions that you have.

 

-Andrew

Cold And Soggy Weekend In The Forecast for Denver

We have had plenty of moisture flow into Colorado over the last two months and it has helped us increase our water tables and keep Colorado out of drought that tends to take hold when we have drier springs. While southeast Colorado is still a bit drier than normal, there isn’t a single location in Colorado designated as being in a drought which is great news to a state that tends to be ravaged by wildfires when droughts take hold. current_usdmIt looks like today and this weekend will help to keep our risk of drought low as we have plenty of cool temperatures and water headed into the state from today through Tuesday. While there is some disagreement on how much moisture we will see, there is agreement that it will be a significant amount and that it will continue for several days.

Current Conditions and Forecast

Snow and rain is beginning to develop around the metro area and is moving into the area from the south as the storm system entering the state begins to spill over the mountains. In the image below, you can see a satellite image of atmospheric water vapor from the GOES West satellite that shows a concentration of moisture from the Pacific Ocean just to the west of Colorado that has started to impact the western slope. Over the next several hours, we will see that concentration of moisture move over the mountains and into the Denver metro area which will increase rain coverage during the day and will lead to occasionally heavy rainfall this afternoon and evening.

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GOES West Satellite Water Vapor Imagery April 28, 2016 8:34 am

Tonight a low pressure center will position itself over southeast Colorado that will aid in bringing moisture to the region through upslope wind flow and our moist beginning to the weekend will continue. Our rain will switch to snow tonight after midnight and should continue as snow through most of tomorrow due to high temperatures only being in the mid 30s. Currently, it looks like most regions will get 1-3″ of snowfall with higher amounts at higher elevations. However, due to our recent warm temperatures, most of the snow will melt off and very little accumulation will actually take place on the ground other than on grassy surfaces.

A fair amount of agreement exists between the models with the total amount of liquid water out of this storm system. One model is saying that we’re looking at roughly 1.5″ of total liquid water and the other is saying roughly 2″. So, there are still some unknowns with this system, but we’re certain that there will be a lot of precipitation. I should mention that the models are suggesting that this will be more of a snow event than I’m predicting, but due to the temperatures and the bulk of the moisture coming when we’re warm, I think they’re erroneous in their prediction.

Final Thoughts

As of right now, it looks like we’ll get the majority of our moisture today and tomorrow, but we’ll continue with cold and soggy conditions through Tuesday with rain falling during the day and snow (or a rain/snow mix) at night. Our temperatures will fall to a minimum tomorrow when highs will only be in the mid 30s. From there, we’ll slowly climb into the 40s on Saturday and Sunday and possibly the low 50s on Monday.

So, prepare for a cold and soggy weekend that will eventually lead to sunny skies, but not before the middle of next week. This type of extended moist and cloudy system is not something that we’re used to dealing with here, but if Seattle can handle it all year long, we can make the best of it for a few days!

 

Thank you for reading!

-Andrew

 

If you want more frequent updates and/or daily forecasts from me, you can download the “My Weather Concierge” app and subscribe to the Denver forecast.

 

Weekend Snow Storm: The Final Forecast

UPDATE: The southern and eastern parts of the metro area have seen significant accumulations with at least one report of 12+ inches in far southeast Centennial. The road and surface temperatures seem to have kept most of the snow from accumulating by melting it once it hits the ground. Based off of radar precipitation accumulations, most areas have already seen between 4-8″ of snow although most of it has melted. 

Over the last week we’ve discussed every aspect of this storm in painstaking detail and
now we get to experience the truly fun part! We get to experience the storm and see whether all of our models, measurements, and analysis was correct or if mother nature will throw us a curve ball. Of course, we always want our forecast to be right. We like to think that we actually understand the atmosphere well enough to make broad predictions that can be used to aid in keeping people safe or, at the very least, making their lives more convenient by giving them the tools to make informed decisions about how they want to address the weather in their daily lives. Nothing feels better than nailing a forecast regardless of whether it’s a snow storm, thunderstorm, or even storm chasing and catching a tornado.

The atmosphere by definition is a chaotic system which means that the smallest force right now can dramatically affect tomorrow or next week’s weather. I’m sure that we all remember the scene from Jurassic Park when Ian Malcolm describes chaos to Dr. Ellie Sattler with the following analogy-

ianmalcolm“It simply deals with unpredictability in complex systems. The shorthand is the Butterfly Effect. A butterfly can flap its wings in Peking and in Central Park you get rain instead of sunshine.”

While that’s an extreme example, the atmosphere is a chaotic system and what may have started as wind from a thunderstorm today, could wind up being a major storm system next week. The unpredictability of it is what makes it so fun. I know plenty of people (most of whom are weather geeks like myself, I must admit) who have been caught in an unexpected rain storm and had it turn into one of their favorite memories.

So, we want our forecast to verify and for our snowfall accumulation predictions to be true, a busted forecast is never a desired outcome, but it’s just another chance to learn about how you can improve in future forecasts. Ultimately, that’s why these storms are so fun! We never truly know what’s going to happen! We will analyze every model run, stare at surface measurements, and launch weather balloons to tell us about the upper atmosphere, but at the end of the day, it’s still just an educated guess and mother nature does not care about the forecast. This is why I tend to go into a frenzy and get (I’ll admit) a bit overly hyped with these big systems! Adventure! The Unknown! Man Vs. Nature! It’s so incredibly fun.

Anyway, enough of the philosophical stuff, ON TO THE FORECAST!

 

I’m going to break down this forecast into four different sections this time:

  1. National Weather Service Winter Storm Warning
  2. Current Information an Storm Timing (including final snowfall accumulation predictions)
  3. Impacts on Travel
  4. Final Thoughts

National Weather Service Winter Storm Warning

...WINTER STORM WARNING REMAINS IN EFFECT UNTIL 6 AM MDT SUNDAY...

* TIMING...MODERATE TO HEAVY SNOW WILL CONTINUE THROUGH SATURDAY
  AND THEN DECREASE SATURDAY NIGHT.

* SNOW ACCUMULATIONS...8 TO 16 INCHES.

* WIND/VISIBILITY...NORTHEAST WINDS 15 TO 30 MPH. VISIBILITY WILL
  FALL TO A QUARTER MILE OR LESS IN HEAVY SNOW AND BLOWING SNOW.

* IMPACTS...ROADS WILL BECOME SLUSHY AND SNOW COVERED...
  ESPECIALLY ON BRIDGES...OVERPASSES AND SECONDARY STREETS. HEAVY
  SNOW ON TREE BRANCHES AND POWER LINES MAY CAUSE THEM TO
  BREAK...POSSIBLY CAUSING POWER OUTAGES. THE SNOW WILL ALSO BE
  HEAVY TO SHOVEL...AND RESIDENTS SHOULD BE CAUTIOUS TO AVOID
  OVER-EXERTION WHILE SHOVELING.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

A WINTER STORM WARNING FOR HEAVY SNOW MEANS SEVERE WINTER WEATHER
CONDITIONS ARE EXPECTED OR OCCURRING. SIGNIFICANT AMOUNTS OF SNOW
ARE FORECAST THAT WILL MAKE TRAVEL DANGEROUS. ONLY TRAVEL IN AN
EMERGENCY. IF YOU MUST TRAVEL...KEEP AN EXTRA FLASHLIGHT...
FOOD...AND WATER IN YOUR VEHICLE IN CASE OF AN EMERGENCY.

Current Information and Storm Timing

Depending on your location around the metro area, you may have already experienced the first bit of this storm. Some light rain had developed on the west side of I-25 this afternoon around 5pm and has slowly tapered to what can be seen in the radar image below. You can see some light rain/snow west of I-25 and the heavier rainfall out east following the severe weather (including tornadoes!) that occurred earlier today.

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Radar Reflectivity at Denver 8:18pm

As we progress tonight, rain/snow showers will increase in coverage between 10-11pm. Thanks to some cloud cover today, we did stay on the cooler side of temperatures and I think that we’ll actually see a switch over to snow a bit earlier than expected. Depending on where you live, you’ll most likely see a full switch over to snow between 10pm and 2am. The snow will increase in intensity over night due to the deepening low that is currently developing over southern Colorado that you can see in the image below. This low, which has counter-clockwise winds, will grab moisture from the Gulf of Mexico and push it up the slope (yes, that’s where the term comes from) of the Rocky Mountains causing the moisture to condense and give us heavy wet snow that will last through Saturday night.

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Low Pressure at 9am on April 16, 2016

While we do have a blocking pattern in place for this storm system, it will be moving out a bit faster than originally expected. Snow will taper off Sunday morning and while some light snow is expected all day, the heavier precipitation will move out to the eastern plains. This is going to decrease our snow totals slightly, but not much. Currently, the Denver metro area is looking at 7-14″ of heavy and wet snow with higher amounts of 9-18″ along the Palmer Divide to the south and the foothills to the west. A lot of this snow will melt when it first starts to fall and it will be so heavy that it will compress under its own weight once it’s on the ground. This means that while 7-14″ of snow may fall, it will probably look like less snow than that.

As I mentioned before, the heavy snow will finish over night on Saturday night which means that these are essentially one day accumulations.

Impacts on Travel

Airlines such as United have already started to cancel flights in anticipation of the storm and many airlines are offering vouchers as rewards for changing your flights in advance. One thing is certain, make sure that you check with your airline before leaving for the airport!

Initial road conditions will most likely be wet due to how warm the temperatures have been, but as heavy snow falls, wet and nasty slush will build up on the roadways eventually. The amount of slush or snow on the roadways obviously depends on how much snow we get and the temperatures which means that I’m not 100% sure just what road conditions will be, but they will most likely deteriorate during Saturday. Travel in the foothills will be nearly impossible as their surface temperatures are colder and they are expected to get much more snow than Denver.

Final Thoughts

While the storm is looking like it will be ~12 hours shorter than expected, we should still see plenty of snow and potentially hazardous conditions. Make sure that you knock off your trees if you get the chance as this will probably be a big branch-breaking storm! I will update on here,  Reddit, and Facebook as conditons change and forecasts are tweaked.

If you want more frequent updates and/or daily forecasts from me, you can download the “My Weather Concierge” app and subscribe to the Denver forecast.

Thank you for reading!

-Andrew

Snow for Denver This Weekend

Well, after waiting for new information on the storm system all week, I can officially say that the original model forecast of snow is looking correct. The snowfall amounts weren’t necessarily correct, but the precipitation type was nailed down pretty well by those early models. As each run has come out, temperatures have been dropped lower behind this storm system and they will, ultimately, lead to a fairly decent amount of snowfall. Currently, the amounts are still up for debate a bit, but Denver and the surrounding areas are currently looking quite a bit of snow and there might be up to three feet in the foothills and elevated terrain.

I’m going to break down this forecast into six different sections this time:

  1. National Weather Service Winter Storm Warning
  2. Storm Timing
  3. Current Information and Data (including preliminary snowfall accumulation predictions)
  4. What Information We’re Waiting On and How It Can Impact The Forecast
  5. Impacts on Travel
  6. Final Thoughts

National Weather Service Winter Storm Warning

THE NATIONAL WEATHER SERVICE IN DENVER HAS ISSUED A WINTER STORM
WARNING...WHICH WILL BE IN EFFECT FROM LATE FRIDAY NIGHT THROUGH
LATE SATURDAY NIGHT.

* SNOW ACCUMULATIONS...ACCUMULATIONS OF 8 TO 14 INCHES WILL BE
  POSSIBLE BY SUNDAY MORNING. THE HIGH DENSITY SNOW WILL TEND TO
  SETTLE AS IT ACCUMULATES...SO THAT SNOW DEPTHS COULD REMAIN LESS
  THAN 8 INCHES.

* WIND/VISIBILITY...NORTH TO NORTHEAST WINDS 15 TO 25
  MPH...ESPECIALLY EAST OF I-25.

* IMPACTS...SNOW-COVERED AND SNOW PACKED ROADS ARE
  EXPECTED...ESPECIALLY ON BRIDGES...OVERPASSES AND SECONDARY
  STREETS. THE SNOW WILL BE A WET AND HEAVY SNOW WITH HIGH LIQUID
  DENSITIES. ACCUMULATING SNOW ON TREE BRANCHES MAY CAUSE TREES TO
  BREAK. THE SNOW WILL ALSO BE HEAVY TO SHOVEL...AND RESIDENTS
  SHOULD BE CAUTIOUS TO AVOID OVER-EXERTION WHILE SHOVELLING.

Storm Timing

The first bits of moisture from this storm system are entering the western part of the state now as rain showers and thunderstorms that you can see in the image below on the Colorado/Utah border. That moisture will begin reaching Denver and the front range tomorrow afternoon when a surface low pressure sets up over the southeastern part of the state and begins developing upslope winds that will sling moisture into the mountains. The storm will intensify over night on Friday night and will continue through Sunday afternoon.

20160414_radar

Radar Reflectivity from Grand Junction, Colorado Showing Rain Showers in Green and Thunderstorms in Yellow and Orange/Red

Current Information and Data

One of the biggest questions about this storm system was “Will it be cold enough to snow?” and that question has been answered over the last few days by each consecutive run of the models. The temperatures have been continually dropped by the models and this will, indeed, be a snow storm. Now, we will probably start as rain tomorrow afternoon and will switch to snow some time over night, but for the remainder of the weekend, we should see primarily heavy and wet snow. The best part of this storm system is that, as many of you have heard me mention in the past, we finally have a blocking feature to keep the storm right on top of us and prevent it from heading east.

Accumulations for this storm depend on two factors, the actual temperature when the snow falls and the amount of moisture available. As a rule of thumb for these spring storms, we generally assume a 10:1 or 8:1 ratio for snow meaning that at colder temperatures we’ll see 10″ of snow for every 1″ of water or, at warmer temperatures, we’ll see 8″ of snow to every 1″ of water in the atmosphere. The models have been shifting a bit with total precipitable water, but we’ve been consistently between 2-3″ of water which would equate to between 16-24″ of snowfall for the warmer temperatures that we’re expecting. If we cool down further, we could be looking at 20-30″. Another complication on top of the already difficult to predict snow totals is trying to time when the rain will switch to snow. If it switches early, obviously accumulations will be higher, a later change to snow will result in less accumulation. Finally, the ground temperatures are extremely warm due to the nice weather we’ve had lately. This means that a lot of the snow that initially falls will most likely melt on the roadways and ground. So, realistically, we’re looking at around 8-16″ around Denver and the front range with much higher amounts to the south and west as we can see in the map below.

Screen Shot 2016-04-14 at 7.34.28 PM

Projected Snowfall Totals Through Sunday Night from the North American Model

What Information We’re Waiting On and How It Can Impact The Forecast

The next couple of model runs will give us our best chance at determining the best predictions for snowfall totals. They should give us a better idea of how much moisture we will have in the atmosphere, how cold our temperatures will be, and how long the system will hang out with us. Depending on how each of these parameters changes with the new runs, snow totals can be altered pretty dramatically. So, do not think that these snow totals are written in stone! They could go up, they could go down.

Impacts on Travel

Beginning on Friday night and continuing through the weekend, travel will be hazardous. Air travel delays and cancellations are a high possibility from Saturday morning through Sunday afternoon which means that checking with your airline before you leave the house is extremely important. Initial road conditions will most likely be wet due to how warm the temperatures have been, but as heavy snow falls, wet and nasty slush will build up on the roadways eventually. The amount of slush or snow on the roadways obviously depends on how much snow we get and the temperatures which means that I’m not 100% sure just what road conditions will be, but they will most likely deteriorate during Saturday. Travel in the foothills will be nearly impossible as their surface temperatures are colder and they are expected to get much more snow than Denver.

Final Thoughts

There is still plenty of time for the forecast to change and for snow accumulations to be altered. This will definitely be a pretty major spring storm, but its impacts are still not fully understood and probably won’t be until we start to experience them. The snow contained in this system will be wet and very heavy which means that you will need to clear it from trees that already have leaves or it will break and destroy branches. We’ll watch the latest runs and make updates as needed with one final forecast update early tomorrow afternoon before the storm hits.

If you want more frequent updates and/or daily forecasts from me, you can download the “My Weather Concierge” app and subscribe to the Denver forecast.

Thank you for reading!

-Andrew

 

Weekend Storm Update

Storm coming! We’re all going to die! OK, not really. It certainly seems like it with the amount of hype going around though. I’ve tried to wait as long as I can to post a follow-up to the forecast from earlier this week in order to make sure that the best information is making it out to everyone, but as we approach the weekend, people are growing a bit restless.

There has been a lot of hype and discussion of this storm system and people want to know what’s actually going to happen. Honestly, we don’t have a whole lot more information than we did when I first posted about it earlier this week, but I’ll do my best to give a brief update of what’s going on currently and what could happen.

Limited Storm Details and Predictions

bou

Winter Storm Watch Area Highlighted in Blue

The National Weather Service has already put out a Winter Storm Warning for the northeastern mountains for Friday afternoon through Saturday night. Snow accumulations for the mountains in the watch area are currently expected to see 12-18″ of snow with wind gusts up to 25 mph.

The same storm that will be impacting the mountains will be impacting the front range and eastern plains as well. The last several runs of the American long and medium range models have dropped the expected temperatures for the storm system which could mean that we will see snow. Now, this system will start on Friday afternoon and could continue through Monday. On Friday afternoon, we will most likely start with rain and switch to snow some time over night or on Saturday morning. The latest model runs have a lot of precipitation in store for us, but that is definitely NOT a certainty.

Predictions

We will definitely get a storm this weekend and it will have a wide range of impacts that will range from rain to snow and even severe thunderstorms with large hail out on the eastern plains. The models agree on the system position fairly well and have it stalling over the top of us which is why they’re predicting so much moisture for the front range. Whether that precipitation is rain or snow and what the amounts will be has yet to be determined. The primary reason for the overall lack of predictions is that this storm system is still out over the northern Pacific ocean and until we can get measurements of it over land with weather balloons and surface stations, we just don’t know enough to really nail anything down.

In conclusion:

  1. Yes, there will be a storm this weekend
  2. No, we don’t know whether it will be a huge snow dump or a rain event (though it’s leaning towards a snow storm)
  3. The models agree on the position and we will, at the very least, see some type of precip
  4. Temperatures are decreasing with each model run which could point to snow for at least part of the event, but that’s far from a certainty
  5. Tomorrow’s model runs will be much more useful because we’ll have better data on the system
  6. It is still too early to make any predictions regarding precipitation amounts

 

I know that this information is not going to satisfy the curiosity over what will happen this weekend, but this is what is currently happening with forecasting the storm. I will make another post tomorrow afternoon with better information and more predictions.

If you want more frequent updates and/or daily forecasts from me, you can download the “My Weather Concierge” app and subscribe to the Denver forecast.

Thank you for reading!

-Andrew

36-44″ of Snowfall in Model Forecasts, but What Can We Really Expect? Rain.

EDIT: This article has gone viral and I want to make perfectly clear that I am not predicting snow as the images posted in other areas make it seem. At this point in time, this looks to be a rain event and I was illustrating how ridiculous the models were acting. You can see the full write-up below without the over-hyped image. Thanks for reading!

There is certainly no shortage of buzz about next weekend’s possible storm system that is poised to hit Colorado. Meteorology forums and forecasters are beside themselves with the possibility of heavy snowfall that this storm contains. One of the reasons that the hype train is already in full effect is that the long range models (GFS, GEFS, ECMWF, and CFS) all have reasonable agreement on the position of the system and the timing, something that hardly ever happens more than a couple days in advance. We have all the great ingredients snow-hype-trainneeded for an epic snow storm with deep upslope wind flow, plenty of moisture in the atmosphere, and a blocking pattern that would keep the precipitation in the region for a few days. With that being said, caution needs to be exercised when talking about this storm because, while there is agreement from the models, there are still far too many variables at play and there is too much time for the models to change before we get to the actual storm.

Storm Overview

A low pressure system will begin to develop over the Rocky Mountain region Thursday and Friday and will move to the east of the Rockies on Saturday and intensify. The storm begins to really sling moisture at us around noon on Saturday and continues through Sunday and into Monday morning. Models have gone crazy with the snowfall on this system predicting up to 45″ of the white fluffy stuff in Denver and the surrounding areas, but this seems absolutely absurd given the temperatures at the time. While winds will be gusty during the event, there is no expectation of a blizzard or heavy snowfall at this point in time.

Primary Concerns With Expecting This To Be A Huge Snow Storm

Proclaiming that this will be an enormous snow storm is foolhardy at this point in time. As we all know, predicting big events like this is very tricky. When warm temperatures and the fact that the storm isn’t expected for another five days come into play, it goes from being tricky to predict to almost impossible. While the models have performed well with several big storms in the continental US over the past winter, they have had their fair share of failures as well.

Pumping the brakes on the hype train is needed due to a few concerns at this time:

  1. While the temperatures are supposed to drop with this system, they are still very warm and, while we still might see precipitation, it would likely fall as rain. The amount of cold air being brought down from Canada doesn’t increase to favorable amounts until a lot of the moisture has already fallen.
  2. Even if the air temperature drops low enough to warrant snowfall, the ground temperatures are still very warm due to the higher temperatures that we experienced last week and will again experience leading up to this event. So, even if snowfall does occur, there is a significant chance that much of it will melt once it hits the ground.
  3. The exact shape and position of the low pressure center is still being resolved and varies from model to model. If it elongates or shifts to the north, we are going to see small amounts of moisture and Wyoming would see more. Even if it ends up as the stereotypical circular cut-off low, it needs to be in the perfect position to give us big snow.
  4. We are still five days out from this event and that is a lot of time for parameters in the models to shift and alter important details of this storm.
    Screen Shot 2016-04-10 at 6.15.20 PM

    Pressure (teal lines) illustrating elongated low with 3-Hour Accumulated Liquid Precipitation at Midnight on Friday night

The Final Word

While the potential of a large accumulation snow storm is certainly exciting, there are still too many unknowns to begin making proclamations about what will actually happen. This will definitely be a storm that we watch over the next few days to determine the likelihood of actually being impacted by it. Making snow or rain accumulation predictions would be foolish at this point and would be anything but accurate, but as the week continues I’ll start putting out rough accumulation predictions as we try to nail down what this storm is actually going to bring us. With that being said, there is nothing to suggest that this will be a big snow event, it will likely be rain and that’s perfectly fine because we need the moisture regardless!

I’ll keep an eye on it and will post updates with new information as it becomes available! If you have any questions or comments, feel free to let me know below!

Snow To Continue Through Evening

Well, this storm was barely a thought in anyone’s mind two days ago. 1-2″ of snowfall was all that was predicted in the weather models and, as time progressed, we saw the models start to agree on the storm system. Unfortunately, that agreement happened late last night at a time when most people had lost interest for the night. Now, the storm is beginning to move out to the east and the large amounts of snow and heavy rates are slowly tapering off.

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Latest Radar Image as of 4:17 pm Showing Snowfall Around the Front Range. Greens and Yellows are Heavier Snowfall.

Admittedly, I was skeptical of the forecast that I saw last night. Twenty inches of snow from a storm that was completely discounted only a few days ago? Most of us had seen this trap before. The latest models said “SNOW”, we got excited, and then nothing happened. This storm took the opposite approach and it has been so much fun! In the upcoming days, I will post an analysis of how we came to understand this storm system and why it caught us by surprise, but in the meantime, let’s just enjoy it.

I would love to see your snow totals and pictures! Feel free to add them on the google map linked below!

SPRING BLIZZARD SNOWFALL TOTALS

If you can avoid traveling, absolutely stay home because you don’t want to be caught up in the road closures and chaos currently unfolding in the picture below.

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